1. Field of the Invention
The present invention relates to a lens control apparatus of a television camera for servo-controlling the position of a focusing lens in accordance with the rotational angle of a rotary handle which is manually operable.
2. Description of Related Art
(1) In television cameras and so on, there have been known lens control apparatuses for servo-controlling the position of a focusing lens for a particular object distance in accordance with an absolute position which is a rotational angle from the mechanical end of a rotary handle. The absolute position of the rotary handle is detected by means of a potentiometer. Further, the lens control apparatus is provided with a sensitivity change-over switch for changing the sensitivity of a focusing-lens control voltage relative to the rotational angle of the rotary handle, and a curve mode change-over switch for changing the relationship between the absolute position of the rotary handle and the focusing-lens control voltage. These switches are disposed at arbitrary positions of the lens control apparatus.
When the sensitivity change-over switch is turned on, the sensitivity of the focusing-lens control voltage relative to the rotational angle of the rotary handle within a prescribed angular range from the absolute position thereof obtained at that time is changed, and, further, when the curve mode change-over switch is switched, the relationship between the absolute position of the rotary handle and the focusing-lens control voltage is changed, so that the position of the focusing lens can be controlled.
(2) There have been known lens control apparatuses for servo-controlling the position of a focusing lens for a particular object distance in accordance with the rotational angle of the rotary handle.
FIG. 20 is a sectional view of a conventional lens control apparatus, and FIG. 21 is a sectional view taken along the line Xxe2x80x94X of FIG. 20. In FIG. 20, a rotary handle 3 is attached to a main body 1 through a bearing 2, and a potentiometer 4 is coupled with the rotating shaft 3a of the rotary handle 3. In addition, a sensitivity change-over switch 5, an LED 6 and a cable connector 7 are disposed at arbitrary positions of the main body 1.
An Archimedean spiral groove 1a as shown in FIG. 21 is formed to the side of the main body 1 which is near to the rotary handle 3 in order to restrict the rotational range of the rotary handle 3. Further, a linear groove 3b is formed in a radial direction to the side of the rotary handle 3 which confronts the spiral groove 1a. A ball 1b is accommodated between the spiral groove 1a and the linear groove 3b. The abutment of the ball 1b against both ends 1c of the spiral groove 1a restricts the maximum number of rotations of the rotary handle 3 to one to three times.
The main body 1 detects the rotational angle of the rotary handle 3 by means of the potentiometer 4 which recognizes it through the rotating shaft 3a of the rotary handle 3. When the sensitivity change-over switch 5 is turned on in this instance, the relationship between the rotational angle xcex8 of the rotary handle 3 and the output voltage V of the potentiometer 4 is changed from a normal mode to a fine-control mode, as shown in FIG. 22. As a result, the sensitivity of the focusing-lens control voltage relative to the rotational angle of the rotary handle 3 is changed within a certain angle range xe2x80x9cxcex8nxc2x1axe2x80x9d about the rotational angle position xcex8n of the rotary handle 3 obtained when the sensitivity change-over switch 5 is turned on. With this operation, the position of the focusing lens can be servo-controlled non-linearly.
(i) However, since the maximum number of rotations (maximum rotational angle xcex8) of the rotary handle 3 is predetermined in the lens control apparatus of the above-mentioned prior art (1), the focusing-lens control voltages V in all the modes must be made identical at each of a starting end and a terminating end of the entire rotating range of the rotary handle 3, as shown in FIG. 23. Accordingly, there is a problem that when the sensitivity of the focusing-lens control voltage is changed from the normal mode to the fine-control mode at a rotational angle xcex81 during process of operation of the focusing lens and, after an optimum position of the focusing lens is obtained at a rotational angle xcex82, the normal mode is resumed, the focusing-lens control voltage V changes from a value Pf to a value Pn, so that the position of the focusing lens will be shifted.
Further, since the focusing-lens control voltage V is determined on the basis of the absolute position of the rotary handle 3, there is a problem that when the curve mode change-over switch is switched from a straight-line mode to a curved-line mode, the focusing-lens control voltage V changes from a value Pb to a value Pa, as shown in FIG. 24, so that the position of the focusing lens will be shifted.
(ii) Since the maximum number of rotations of the rotary handle 3 is predetermined also in the lens control apparatus of the above-mentioned prior art (2), focusing-lens control voltages Vo at a starting end of the rotary handle 3 in all the modes or focusing-lens control voltages Ve at a terminating end of the rotary handle 3 in all the modes must be made always identical, as shown in FIG. 22. Therefore, the lens control apparatus has a problem that when the sensitivity of the focusing-lens control voltage is switched from the normal mode to the fine-control mode at the rotational angle position xcex8n during process of operation of the focusing lens and, after an optimum position of the focusing lens is obtained at the rotational angle xe2x80x9cxcex8n+axe2x80x9d, the normal mode is resumed, the focusing-lens control voltage changes from a value Vb to a value Va, so that the position of the focusing lens will be shifted.
An object of the present invention is to solve the above problem (i) and provide a lens control apparatus in which, even if the mode of the sensitivity of a focusing-lens control voltage relative to the rotational angle of a rotary handle is changed over, the focusing-lens control voltage is not varied and, hence, the position of a focusing lens is not shifted.
Another object of the present invention is to solve the above problem (ii) and provide a lens control apparatus in which, even if the mode of the sensitivity of a focusing-lens control voltage relative to the rotational angle of a rotary handle is changed over, the position of a focusing lens is not shifted, and the sensitivity of the focusing-lens control voltage can be obtained in two types of modes.
To attain the above objects, in accordance with an aspect of the present invention, there is provided a focusing lens control apparatus, which comprises a rotary operation member, a measuring circuit, having a rotary encoder coupled with the rotary operation member, which counts number of pulses per unit time outputted from the rotary encoder, and a conversion circuit which converts a measurement output of the measuring circuit into a position signal indicative of a position of a focusing lens, wherein the position of the focusing lens is controlled on the basis of the position signal outputted from the conversion circuit.
Further, to attain the above objects, in accordance with another aspect of the present invention, there is provided a lens control apparatus, which comprises a rotary operation member, state detecting means for detecting a rotating state of the rotary operation member, a conversion circuit which converts a detection signal provided by the state detecting means into a position signal indicative of a position of a lens, the lens being driven on the basis of the position signal outputted from the conversion circuit, and conversion characteristic changing means for changing a conversion characteristic of the conversion circuit.
These and further objects and features of the present invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.